Plastic fasteners (also commonly referred to in the art as plastic attachments) are well known in the art and commonly used to couple articles of commerce to packaging, buttons to fabric, merchandising tags to articles of commerce, or, in general, any two desired articles. One type of plastic fastener which is widely used in commerce is manufactured in an H-shaped configuration, with two shortened parallel cross-bars, or T-bars, interconnected at their approximate midpoints by a thin, flexible filament that extends orthogonally therebetween.
Plastic fasteners of the type described above are commonly fabricated as part of continuously connected ladder stock that is produced from one or more flexible plastic materials, such as nylon and polypropylene, using conventional molding or stamping techniques. Referring now to FIG. 1, there is shown a length of continuously connected ladder stock 11 that is well known in the art. Ladder, or fastener, stock 11 is formed from two elongated and continuous plastic side members, or rails, 13 and 15 that are interconnected by a plurality of equidistantly spaced cross-links, or filaments, 17. By severing each of side rails 13 and 15 at the approximate midpoint between successive filaments 17, a plurality of individual plastic fasteners 18 can be produced from ladder stock 11. Each plastic fastener 18 produced from ladder stock 11 comprises a pair of cross-bars 19 and 21 that are interconnected by a thin, flexible filament 23, with cross-bars 19 and 21 being derived from side rails 13 and 15, respectively, and filament 23 being derived from a corresponding cross-link 17. Ladder stock of the type described above is shown in U.S. Pat. No. 4,039,078 to A. R. Bone and U.S. Pat. No. 5,615,816 to C. L. Deschenes, the disclosures of both patents being incorporated herein by reference.
Ladder stock of the type described above is presently manufactured and sold by Avery Dennison™ Corporation of Pasadena, Calif. under the Plastic Staple® and Elastic Staple™ lines of plastic fasteners. The commercialized ladder stock is traditionally wound onto a reel, or spool, which is sized and shaped to hold a supply of ladder stock that yields approximately 25,000 fasteners.
Either manually or with the aid of specifically designed devices, individual fasteners are commonly severed from a supply of ladder stock and, in turn, dispensed in order to secure together two or more items. One well known automated device for dispensing individual plastic fasteners from a reel of ladder-type fastener stock includes a pair of hollow needles that are adapted to penetrate through one or more items, a feed mechanism for advancing each rail of the supply of ladder stock into axial alignment behind the longitudinal bore defined by a corresponding hollow needle, a severing mechanism for severing a fastener to be dispensed through the pair of hollowed needles from the remainder of the ladder stock, and an ejection mechanism for ejecting the cross-bars of the severed fastener through the bores of the pair of hollowed needles and, in turn, through the particular items that are penetrated by the needles.
For example, in commonly assigned U.S. Pat. No. 5,433,366, which is incorporated herein by reference, there is disclosed a device for dispensing plastic attachments from a roll of continuously connected ladder stock. In one embodiment, the device includes a pair of hollow slotted needles, each needle having a sharpened tip, a rear end and a longitudinal axis. A feed wheel, placed proximate to the rear ends of the pair of needles, is used to feed the side rails of the ladder stock into the pair of needles through their respective rear ends at angles relative to the longitudinal axes thereof. Once inserted into the needles, an attachment is severed from the remainder of the ladder stock by a knife and is then expelled from the needles by a pair of ejector rods movable along the longitudinal axes of the pair of needles. Because attachments are fed into the pair of needles at angles relative to their longitudinal axes, no shuttling of the needles between an attachment feeding position and an attachment ejection position is required. The pair of needles, the feed wheel, the knife, and the pair of ejector rods are all mounted on a vertically movable head member, or head. An induction motor is used to move the head member between an attachment dispensing position and a withdrawal position. The vertical movement of the head member drives the operation of the feed wheel, the knife and the ejector rods.
As noted briefly above, fasteners of the type as described above are commonly used in a wide variety of different applications to secure together two or more items. For example, fasteners of the type described above are commonly used in packaging applications to secure an article of commerce to a display card. As part of the securement process, the display card is first positioned on an anvil for the fastener dispensing machine. Next, the article of commerce is placed in its desired location on the top surface of the display card. Upon actuation of the machine, the pair of needles penetrates through the display card on opposite sides of the article of commerce and in close proximity relative thereto. As a fastener is severed from the fastener stock and subsequently ejected through the hollow needles, each of the pair of cross-members engages the underside of the card with the thin filament stretching tightly across the front of the article. In this capacity, the dispensed fastener serves to secure the article to the display card in an inconspicuous and unobtrusive manner.
In certain applications, it has been found to be desirable to modify the spacing between the pair of needles for fastener dispensing devices of the type described above. For instance, adjusting the spacing between needles is often required to accommodate supplies of ladder stock with cross-links of varying lengths (e.g., between 0.25 inches and 0.38 inches). In addition, adjusting the spacing between needles is often required to account for variances in the size and shape of articles that are commonly joined using plastic fasteners (e.g., items of different widths that are secured to display cards).
Accordingly, fastener dispensing devices with variable needle spacing are known in the art. Referring now to FIG. 2, there are shown selected components for a prior art device for dispensing individual plastic fasteners from a supply of ladder stock, the fastener dispensing device being identified generally by reference numeral 31. As can be seen, device 31 includes a pair of needles 33-1 and 33-2 that are individually coupled to a motor-driven shuttle 35 by corresponding, mirror image, needle block assemblies 37-1 and 37-2, respectively. As can be appreciated, the lateral position of at least one needle block assembly 37 is adjustable to enable the spacing between needles 33 to be modified as needed. In addition, it should be noted that needle block assemblies 37-1 and 37-2 not only serve to retain needles 33 but also include guide channels 39-1 and 39-2, respectively, that assist in positioning side rails 13 and 15 of ladder stock 11 that are fed into device 31 into proper alignment behind hollow needles 33.
Although well known and widely used in commerce, fastener dispensing devices with variable needle spacing capabilities have been found to suffer from a notable drawback. Specifically, when needles 33 are drawn relatively close to one another, filaments 17 tend to distort (i.e., bow, twist and/or loop) in a random, irregular pattern, as shown in FIG. 2. When a fastener dispensing device with closely spaced needles is used in high speed dispensing applications, the presence of irregularly patterned filament distortions in the ladder stock has been found to significantly increase the likelihood of jamming. Once a jamming condition occurs, the fastener dispensing device needs to be shut down until a relatively labor-intensive and time-consuming repair can occur to remove the jammed ladder stock, which is highly undesirable.